JPS6234768B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing novel tetrafluoroethylene (TFE) micropowder resins, and in particular to such resins having good stretching performance. Tetrafluoroethylene (TFE) micropowder resins are non-melt-fabricable and are typically produced by mixing the powder with a lubricant and then extruding it through a paste extruder. It is processed by paste extrusion, which consists in obtaining films, tubes, tapes, protective coatings on wires, etc. Such paste-extruded films, tubes, and tapes can be rapidly stretched in an unsintered form and are porous to water vapor but not liquid water. It is not possible to form a strong material. Such materials are useful in providing "breathable" textile materials for kimonos, gauze tenting, separation membranes, and the like. Heretofore, resins useful for making such paste extruded stretched films have been limited to lubricant loading levels and also to ensure good stretched products over the loading levels used. It showed sensitivity to extension speed, which required careful control. Improved, less sensitive to lubricant load levels and has improved extensibility
It would be desirable to improve upon these known resins by providing TFE micropowder resins. The present invention relates to a method for obtaining these. The present invention comprises tetrafluoroethylene and optionally a small amount of selected copolymerizable fluorinated ethylenically unsaturated comonomers present in an aqueous medium in an amount that maintains the colloidal particles of the polymerization product in dispersed form. a method for producing a tetrafluoroethylene resin by polymerization in the presence of a substantially non-telogenic anionic surfactant, the method comprising: The comonomer is combined with (i) a manganese triacetate oxidizing agent, and (ii) a substantially non-telogenic reducing agent (preferably this reagent is oxalic acid, malonic acid, citric acid, divalent iron, sodium bisulfite, thiosulfuric acid, etc.). in the presence of a redox polymerization initiator system, defined as a mixture of sodium sulfate, hydroxylamine, hydrazine or mixtures thereof, wherein The agent system is used as a preliminary load.
or added intermittently or continuously, in which case the last addition stalls the reaction compared to the reaction if the initiator addition was continued until the end of the polymerization.
A method is provided which consists in performing such that the end point is longer by at least 10%, preferably by 20%. By this method, an aqueous dispersion of resin is produced. A resin is obtained upon flocculation of the dispersion. This resin has unusual insensitivity to lubricant loading levels and high stress relaxation times (dwelling times).
dwelltime) and have a low decompression rate, e.g. per second
It can be stretched by 10% to produce porous articles. The dispersions are useful for coating metals and textiles. The polytetrafluoroethylene obtained by the method of the invention is referred to by those skilled in the art as "Fine Powder" tetrafluoroethylene resin. The phrase "fine powder" has acquired a special meaning in this field. This is because the resin undergoes “aqueous dispersion polymerization”.
polymerization”). In this method, sufficient dispersant is used to produce particles of small colloidal size that are dispersed in an aqueous reaction medium and agitated Sedimentation (i.e. agglomeration) of resin particles is avoided during polymerization. Little or no dispersant is used and stirring is vigorous to produce a precipitated resin. There is another type of polytetrafluoroethylene material called "Granular" polytetrafluoroethylene, which is produced by polymerizing tetrafluoroethylene by a process consisting of: This method is called "suspension polymerization." These two polymerization procedures produce dramatically different products. “Granular” products can be molded into a variety of shapes, whereas products made by aqueous dispersion processes cannot be molded and can be disperse coated or agglomerated. A fine powder can be obtained and then processed by adding a lubricant to the powder for paste extrusion. In contrast, particulate resins cannot be paste extruded. Tetrafluoroethylene can be polymerized alone in the method of the present invention to obtain the finely powdered homopolymer resin of the present invention. Additionally, tetrafluoroethylene can be copolymerized with a copolymerizable fluorinated ethylenically unsaturated comonomer under conditions that the amount of comonomer is not sufficient to render the resulting polymer melt-fabricable. can be done. Typical copolymerizable fluorinated ethylenically unsaturated comonomers have the following formula:

【formula】

[expression] or

[Formula] _In the formula _, R ₁ is R _f , _{-R f} is a fluoroalkyl group, and -R _f - is
A linear perfluoroalkylene diradical of 1 to 10 carbon atoms with bond valencies at each end of the linear chain, and X is H or Cl and R ₂ is F, -R _f or - R _f −X and R ₃ is H or F. The following formula In the formula, Y is

[expression] or

[Formula], X and X' are F or Cl, Z and
Dioxoles may also be used, in which Z' is each alkyl or fluorinated alkyl of 1 to 6 carbons. Typical copolymerizable fluorinated ethylenically unsaturated comonomers include hexafluoropropylene, perfluorohexene-1, and perfluorononene-1.
1. Perfluoro(methyl vinyl ether), perfluoro(n-propyl vinyl ether), perfluoro(n-heptyl vinyl ether), perfluoromethylethylene, perfluorobutylethylene, ω-hydroperfluoropentene-
Mixtures of these are included, such as 1,3-hydroperfluoro(propyl vinyl ether) or a mixture of hexafluoropropylene and perfluoro(propyl vinyl ether). Preferably the comonomers are perfluoro(alkyl vinyl ethers) of the formula R _f -O-CF=CF ₂ , or perfluoro(terminally unsaturated olefins) of the formula R _f -CF=CF ₂ , or perfluoro(terminally unsaturated olefins) of the formula R _f -CH = CH ₂ selected from perfluoroalkylethylenes, in the formula R _f
is perfluoroalkyl of 1 to 10 carbon atoms. By the phrase "non-melt processable" is meant a tetrafluoroethylene polymer whose melt viscosity is so high that the polymer cannot be easily processed by melt processing methods. Generally, the higher the molecular weight of the polymer, the higher the melt viscosity. The melt viscosity above which tetrafluoroethylene polymers become non-melt processable is 1×10 ⁹ poise. Because the melt viscosity of non-melt processable polymers is very high, molecular weight is usually measured indirectly by procedures that give the standard specific gravity (SSG) of the resin. of resin
SSG changes inversely with molecular weight; as molecular weight increases, the SSG value decreases. The resins produced herein generally have the following properties: (a) primary particle size between 0.1 and 0.5 μm, (b) non-surface area greater than 5 m ² /g, (c) standard specific gravity. is less than 2.190, (d) rheometric pressure
(sometimes referred to as extrusion pressure) is at least 250 Kg/cm ² at a Reduction Ratio of 400:1; (e) uniformity of elongation throughout the 4% by weight lubricant loading range; at least 75% and this 4% by weight range at a stretching rate of 100%/sec.
Lubricant loading levels should range between 10 and 20% by weight. (f) The uniformity of elongation is at least 75% over elongation rates between 10 and 100%/sec at a lubricant loading level of 17%. (g) Stress relaxation time is at least 400 seconds, measured at 393°C. In a preferred embodiment, the uniformity of stretching is
17-20% by weight at a stretching rate of 100%/s
and at least 75% over the entire lubricant load range between 22% and 100%/sec at 17 wt. %. In the process of the invention, the tetrafluoroethylene monomer, optionally together with an ethylenically unsaturated comonomer, is mixed with or contacted with an aqueous medium containing a dispersant and a polymerization initiator. Polymerization temperature and pressure are not critical using the reaction profile described above. Temperatures useful to decompose the Mn ⁺³ initiator system are desirable for the purpose of obtaining high molecular weight near the surface of the resin particles produced. Ideally, the temperature should be between 50° and 125°C, preferably 65°C.
The temperature should be between ゜～100℃. The practical pressure is not critical, but may be between 15 and 40 Kg/ ^cm2 , preferably between 25 and 40 Kg/ ^cm2 . Polymerization is usually carried out in a gently agitated autoclave. The dispersant used should be anionic and substantially non-telogenic. Commonly used dispersants are fluorinated carboxylates, such as ammonium polyfluorocarboxylates, containing 7 to 20 carbon atoms.
The amount of dispersant present should be sufficient to stabilize the colloidal dispersion. It is usually based on the weight of water used in the aqueous dispersion.
It can be between about 1000 ppm and about 5000 ppm. Dispersants can be added prior to the initiation of polymerization or can be added in increasing amounts as described in Punderson, US Pat. No. 3,391,099. If desired, paraffin waxes (i.e. saturated hydrocarbons having more than 12 carbon atoms) which are liquid at the polymerization temperature can be prepared using a Bankoff
No. 2,612,484.
Normally, this wax contains 0.1% of the water in the aqueous dispersion.
Only amounts between ~12% by weight are used. Polymerization is carried out by mixing the components under the conditions specified above. Mixing is usually accomplished by gently stirring the aqueous polymerization mixture. The agitation is controlled to serve to prevent premature agglomeration of the resin particles formed during polymerization. Polymerization is typically carried out so that the solids level (i.e., polymer content) of the aqueous mixture is approximately 15 to 60% by weight of the mixture.
This is done until the end of the period. The phrase "substantially non-telogenic" used in the definition of dispersant ensures that the polymer produced is produced under the same conditions but using ammonium perfluorooctanoate as a dispersant. It is meant to have an SSG that is at most 0.010 larger than the SSG of the polymer. (SSG is a measure of the molecular weight of a polymer). Similarly, with respect to reducing agents, the term nontelogenic means that the polymer produced has an SSG that is no more than 0.010 greater than the SSG of a polymer produced under the same conditions but using oxalic acid as the reducing agent. It means that. The initiator may be present, optionally as a preload and/or in bulk during the polymerization, provided that the selected reducing agent, preferably oxalic acid, is present to form a redox group with the manganese triacetate. , or continuously to the polymerization vessel. The amount of manganese triacetate used is between 5 and 500 ppm, preferably between 25 and 500 ppm, based on the aqueous loading, depending on the molecular weight desired in the polymer.
Between 100ppm. The amount of reducing agent used is
It is again 5 to 500 ppm, preferably 25 to 100 ppm, based on the aqueous loading. The reaction is generally carried out in an acidic medium. Succinic acid is a common acid and is preferred as it also prevents agglomeration. Buffers may be used to control the PH. Upon completion of polymerization, the dispersed polymer particles may be agglomerated by high speed stirring. The particles can then be collected and dried. The non-melt processable tetrafluoroethylene fine powder resin produced by the method of the present invention exhibits excellent elongation performance at elevated temperatures, e.g. 300°C;
The result is a stretched material that is strong and breathable, but impermeable to liquid water. The resin is of high molecular weight, less than 2.190
Has SSG. These things should be at least 250
High rheometer pressure (Kg/ ^cm2)
pressure). These things are 0.1 to 0.5
It has a primary particle size between μm. By the phrase "primary" is meant the size of the colloidal resin particles as measured prior to aggregation. This resin is
It also has a specific surface area greater than 5 m ² /g. Additionally, the resins of the present invention have some unusual elongation properties. First, the resin can be paste extruded over a wide range of amounts of lubricant additives present. Typically, fine powder resins are sensitive to the amount of lubricant present during paste extrusion, and as the amount varies, the properties of the paste extrusion product vary widely. Uniquely, with the resins of the present invention, the amount of lubricant can be varied widely, e.g., within the overall range of 10% to 20% by weight, from at least a load range of 4% and above, elongation A speed of 100%/sec can be varied without any noticeable loss in stretch uniformity and surface smoothness. This is an insensitivity to organic lubricant loading levels not commonly found with other fine powder resins. Suitable organic lubricants include:
Included are hexane, heptane, naphtha, toluene, xylene, and kerosenes such as Isopar K and E. Generally, these lubricants have a viscosity of at least 0.3 centipoise at 25°C and are liquids under extrusion conditions. Preferably, these will contain paraffins, naphthenes and aromatics and small amounts of olefins. Furthermore, the resins of the present invention exhibit unusual insensitivity to elongation rate. Most fine powder resins exhibit poorer elongation performance as the elongation rate is reduced. Surprisingly, however, when the stretching rate of the resin of the present invention was varied between 10% per second and 100% per second, the stretched product showed a lubricant loading level of 17%.
There was no significant change in stretch uniformity or surface smoothness in weight percent. Specifically, the uniformity of elongation was at least 75%. This means that the ink marks placed in the center of the paste extruded beads prior to stretching did not move more than 25% from the center of the stretched product. Additionally, the stress relaxation times of the resins of the present invention are significantly greater than those for most other fine powder resins. The resins of the present invention are useful in any paste extrusion application in which known finely powdered tetrafluoroethylene resins are useful. Test Procedure 1 Original Dispersion (Primary) Particle Size (Avg) RDPS was determined from the absorbance (scattering) of a dilute aqueous sample at 546 mμm using a Beckman DU spectrophotometer, as described in U.S. Pat. No. 4,036,802. This is based on the principle that the turbidity of a dispersion increases as the particle size increases, as shown in . 2 Standard Specific Gravity (SSG) SSG was measured by water displacement of standard molded specimens according to ASTM D1457-69. The standard molded part is preformed with 12.0 g of powder in a 2.86 cm diameter mold at a pressure of 352 Kg/ ^cm2 , followed by 300 kg/cm2 pressure.
This preform is subjected to a sintering cycle of heating from 380 °C to 380 °C at 2 °C/min, holding at 380 °C for 30 minutes, cooling at 1 °C/min to 295 °C, and holding at this temperature for 25 minutes. The specimen was then cooled to 23° C. and its specific gravity was measured. 3 Rheometer Pressure Rheometer pressure was ASTM, except that the resin was not screened prior to mixing with the kerosene lubricant and the preform was made at 300 psi in a 26 mm diameter draw tube.
Measured according to D1457-81A, Section 12.8. A Reduction Ratio of 400:1 was used. 4. Specific surface area (SSA) SSA is kanta. chromium. Coop (Quanta
Measurements were made on a "Quantasorb" surface area analyzer sold by Chrome Corp. The analyzer was calibrated by BET method. 5 Stretch test a Manufacture of test piece A resin sample was sieved through a 2000 μm sieve. 100 g of this resin was mixed with the desired amount of Isopar K lubricant at room temperature by shaking in a glass jar with an internal diameter of 6 cm and spinning at 64 rpm for 4 minutes. This was then preformed at 400 psi in a 26 mm diameter x 23 cm long tube at room temperature. The preform was then paste extruded at room temperature into uniform beads through a 2.4 mm diameter orifice. The length of the orifice land was 5 mm. The extrusion speed was 84 cm/min. The angle of the mold was 30°. Beads were dried at 190°C for 20 minutes. b. Stretch test Beads of resin were cut and clamped at each end, leaving a 50 mm space between the clamps, and heated to 300° C. in a circulating air oven. The clamp was then moved at the desired speed to the desired length and released. The stretched specimens were examined for uniformity of stretch, flat appearance, and surface roughness. The % uniformity was calculated as follows: % Uniformity of Stretching = 100 x nearer distance from ink mark to bead end after stretching/1/2 of total length after stretching 6 Stress Relaxation Time The specimen for relaxation time measurement consists of beads,
As in the stretch test, this was done by stretching at 1000%/sec to a total stretch of 2400%. The stress relaxation time is under the condition that this specimen is stretched.
This is the time required for the material to break when heated to 393℃. During the short period when the specimen is placed in the oven, the temperature drops somewhat, for example to 375°C, and it takes about 1 minute for the oven to return to 393°C. Stress relaxation time is the time starting from placing the specimen into the oven. Examples Example 1 Into 36 polymerization reactors (polykettle), 19.1 kg of deionized water, 600 g of paraffin wax, 16 g of ammonium perfluorooctanoate (C-8) dispersant, 0.15 g of zinc chloride, and 1.0 g of oxalic acid. and 3 g of succinic acid. The contents of the polymerization reactor
Heat to 70°C, degas and TFE purge. The contents of the polymerization reactor were stirred at 46 RPM. The temperature was increased to 80°C. TFE then pressure
It was added until it reached 2.75×10 ⁶ Pa. A fresh solution of 3.2 g of manganese triacetate, manganese acetate () dissolved in 1000 ml of water-acetic acid mixture (1:1 volume ratio) was added at 6.5 ml/ml until 8.2 Kg of TFE had reacted.
injected at a rate of 1 minute. Polymerization started 4 minutes after the beginning of the initiator injection, as evidenced by the drop in pressure. TFE to maintain pressure at 2.75×10 ⁶ Pa
added. After 0.9 Kg of TFE had reacted, a solution of 42 g of ammonium perfluorooctanoate in 1000 ml of water was pumped in at 50 ml/min. The total manganese salt added was 0.768g. 67%
No manganese triacetate was added after the TFE had been polymerized. The reaction was 58% longer than it would have been if the Mn salt addition had continued to the end. After 12.3 Kg of TFE had reacted, the feed was stopped and the polymerization reactor was vented, evacuated, and purged with _N2 . The contents were cooled and emptied from the polymerization reactor. The supernatant wax was removed. The dispersion was diluted to 15% solids and flocculated in the presence of ammonium carbonate under high stirring conditions. The aggregated fine powder was separated and dried at 150-160°C for 3 days. Polymer properties are given in Tables 1 and 2. The stretching performance was excellent. The total reaction time from TFE pressure increase to supply stop is compared to operation A.
(below) compared to 123 minutes. Comparative operation A: Add 20 ml of deionized water to the polymerization reactor described in Example 1.
Kg, paraffin wax 600g, APFC (C-
8) Loaded with 13g surfactant and 10g succinic acid. After obtaining a TFE pressure of 2.75×10 ⁶ Pa, add 120 ml of ammonium persulfate (APS) solution (1.0 g/)
was added at 100 ml/min at 75°C. After 0.9 Kg of TFE had reacted, a further solution of 45 g of C-8 in 1000 ml of water was pumped in at 50 ml/min. The temperature was maintained at 75°C. After 14.1 Kg of TFE had reacted, the feed was stopped and the polymerization reactor was allowed to react down to 1.72×10 ⁶ Pa before venting. After processing as in Example 1, a fine powder was obtained. Polymer properties are given in Tables 1 and 2. Although the stretching performance is good, the total reaction time is
It took 123 minutes. In this example, if a commonly used initiator such as APS is used, in order to obtain satisfactory stretching performance,
This shows that the reaction time is substantially longer than that of the manganese salt. Comparative Procedure B Example 1 was repeated, except that the manganese triacetate solution was continuously injected until the end of the polymerization. The total manganese salt added was 1.267 g. The total reaction time is
It took 61 minutes. The stretch piece broke during stretching. Polymer properties are given in Tables 1 and 2. This example shows that the polymer extension performance is unsatisfactory when the initiator is injected until the end of the polymerization, resulting in a lower molecular weight relative to the particle envelope. Comparative Procedure C Example 1 was repeated except that oxalic acid, succinic acid and ZnCl ₂ were not used. No reaction occurred. In this example, in the absence of a reducing agent, TFE
This shows that no polymerization occurs.

【table】

【table】

Claims (1)

Claims: 1. Tetrafluoroethylene and optionally small amounts of selected copolymerizable fluorinated ethylenically unsaturated comonomers to maintain colloidal particles of the polymerization product in a dispersed form in an aqueous medium. The method comprises polymerizing tetrafluoroethylene and the optional comonomer in the presence of a substantially non-telogenic anionic surfactant present in an amount of (i) manganese triacetate oxidation. and (ii) a redox polymerization initiator system, defined as a mixture of a substantially non-telogenic reducing agent, in the aqueous medium, wherein the initiation The agent system is added, optionally as a precharge, or intermittently or continuously, in which case the last addition causes a reaction that stalls and the initiator addition continues until the end of the polymerization. method, consisting of performing the test in such a way that the end point is at least 10% longer. 2. A process according to claim 1, comprising the absence of any optional comonomers. 3. There are comonomers that may optionally be used, which are represented by the formula [Formula] [Formula] or [Formula] where R ₁ is -R _f , -R _f -X', -O-R _f Or -O-R _f -
X', in which -R _f is a perfluoroalkyl group of 1 to 10 carbon atoms, -R _f
- is 1 with bond valences at each end of the linear chain
A linear perfluoroalkylene diradical of ~10 carbon atoms, and X' is H or Cl, R ₂ is F, -R _f or -R _f -X, and R ₃ is H or F, or the following formula In the formula, Y is [Formula] or [Formula], X and X' are F or Cl, and Z and
2. The method of claim 1, wherein Z' is an alkyl of 1 to 6 carbons or a fluorinated alkyl. 4 The reducing agent is oxalic acid, malonic acid, citric acid,
A method according to claim 1, comprising divalent iron, sodium bisulfite, sodium thiosulfate, hydroxylamine, hydrazine or a mixture thereof. 5. The method according to claim 1, wherein the reducing agent is oxalic acid.